Relative contribution of Artemia and mussel as food for cultured middle‐stage Panulirus japonicus phyllosomata as determined by stable nitrogen isotope analysis

Abstract

Artemia and mussel gonad represent the main food items in the culture of phyllosomata, including those of the Japanese spiny lobster, Panulirus japonicus. It remains unclear, however, to what extent phyllosomata consume and assimilate these two food items because it is difficult to estimate their food intake by conventional observation methods. In this study, we used stable nitrogen isotope analysis to estimate the relative assimilation of Artemia and mussel (Mytilus galloprovincialis) gonad by cultured phyllosomata, based on the assumption that the heavier nitrogen isotope (¹⁵N) is enriched in the bodies of phyllosomata during assimilation and metabolic processing of foods, resulting in an increased δ¹⁵N value. First, subadult and adult Artemia and mussel gonad were sampled monthly to examine the difference in δ¹⁵N between the two food items. Artemia and mussel gonad had δ¹⁵N values of ‐0.2‰ ± 0.6‰ and 9.8‰ ± 0.8‰ (mean ± SD), respectively. Using δ¹⁵N measurements of phyllosomata 29 days after hatching and cultured on a diet of Artemia, the fractionation value of the phyllosomata was calculated as 2.5‰. Middle‐stage phyllosomata (99 days old, body length = 9.3 ± 0.5 mm, n = 4) cultured with mixed diets of Artemia and mussel gonad had δ¹⁵N values of 5.7‰ ± 0.4‰. Calculations based on these measurements indicated that 66% of all nitrogen in the bodies of the phyllosomata were derived from Artemia and 34% from mussel gonad, suggesting that Artemia is the more important food item for phyllosomata with a body length of c. 10 mm and at least 99 days of age. Our results indicate that the analysis of stable nitrogen isotope ratios is a useful diagnostic tool to estimate the relative assimilation rates of different food items.

Keywords:

• lobster
• phyllosoma
• culture
• Mytilus galloprovincialis